The present application relates to a liquid crystal display device including a liquid crystal display element in which a liquid crystal layer is formed in a sealed-off state between a pair of substrates having alignment films formed on substrate surfaces opposing to each other. The present application also relates to a method for manufacturing the liquid crystal display device.
Recently, LCDs (Liquid Crystal Displays) have been used as display monitors for liquid crystal television receivers, notebook-size personal computers, car navigation devices, etc. in many cases. The liquid crystal displays are classified into various display modes (types) depending on molecular arrangement (alignment) of liquid crystal molecules that are contained in a liquid crystal layer formed in sandwiched relation between substrates. As one example of the display modes, there is a TN (Twisted Nematic) mode in which liquid crystal molecules are arrayed while twisting in a state not applied with a voltage. In the TN mode, each liquid crystal molecule has positive dielectric anisotropy, i.e., a property that the dielectric constant of the liquid crystal molecule in its major axis is larger than that in its minor axis. Therefore, the liquid crystal layer is of such a structure that the liquid crystal molecules are successively arranged in a line in the direction perpendicular to the substrate surface while the oriented azimuths of the liquid crystal molecules are gradually rotated in planes parallel to the substrate surface.
On the other hand, attention has been focused on a VA (Vertical Alignment) mode in which the liquid crystal molecules are aligned in vertical orientation perpendicularly to the substrate surface in the state not applied with a voltage. In the VA mode, each liquid crystal molecule has negative dielectric anisotropy, i.e., a property that the dielectric constant of the liquid crystal molecule in its major axis is smaller than that in its minor axis. Therefore, the VA mode can realize a wider viewing angle than the TN mode.
In the liquid crystal display of the VA mode, when a voltage is applied, the liquid crystal molecules aligned in vertical orientation perpendicularly to the substrate surface responds to the applied voltage such that the molecules are tipped down to the direction parallel to the substrate surface due to the negative dielectric anisotropy, thus allowing light to pass through the liquid crystal layer. However, because the liquid crystal molecules aligned perpendicularly to the substrate surface are tilted in arbitrary directions, the alignment of the liquid crystal molecules is disturbed upon the application of the voltage, whereby a response characteristic to the voltage is degraded.
Techniques for restricting the direction in which the liquid crystal molecules are tilted in response to the voltage have been studied with the view of improving the response characteristic. More specifically, there is a technique (photo-alignment technique) in which a pre-tilt is given to the liquid crystal molecules by using an alignment film that is formed by casting linearly-polarized ultraviolet light or obliquely casting ultraviolet light for irradiation to the substrate surface. In one example of the photo-alignment technique, an alignment film is formed by obliquely casting linearly-polarized ultraviolet light for irradiation to a film, which is made of a polymer including a chalcone structure and which is formed on the substrate surface, so that a double-bond portion in the chalcone structure is cross-linked (see Japanese Unexamined Patent Application Publication No. 10-087859, No. 10-252646, and No. 2002-082336). As another example, there is a technique of forming an alignment film by using a mixture of a vinyl-cinnamate derivative high-molecule and polyimide (see Japanese Unexamined Patent Application Publication No. 10-232400). As still another example, there is a technique of forming an alignment film by casting linearly-polarized ultraviolet light at a wavelength of 254 nm for irradiation to a film containing polyimide, thereby decomposing part of the polyimide (see Japanese Unexamined Patent Application Publication No. 10-073821). Further, as one example in peripherals of the photo-alignment technique, there is a technique of forming a liquid crystal alignment film by forming a film made of a liquid crystal high-molecular compound on a film made of a polymer containing a dichroic photo-reactive formation unit, e.g., an azobenzene derivative, after casting linearly-polarized ultraviolet light or oblique light for irradiation to the latter film (see Japanese Unexamined Patent Application Publication No. 11-326638).